Projection screen



E. A. TROEGER PROJECTIQN SCREEN Aug. 7, 1934.

Original Filed Dec. 1'7

l uwram-o` y A TOR EY Patented Aug. 7, i934 STATES PATENT; OFFICE- 1,969,485 PROJECTION SCREEN Application December 17, 1926, Serial No. 155,407

Renewed May 27, 1932 i Claims.

This invention relates to a projection screen of the translucent type in which the image is projected upon the side of the screen opposite to the side which is viewed by the audience. The

5 object of my invention is to provide a screen of that type which may be easily and cheaply made and which will effectively diffuse light striking the screen so as to avoid a glaring bright spot,

which is so common with other screens of thisl0 nature. Further objects and advantages will appear during the following description of my invention when taken in conjunction with the accompanying drawing, in which Figure 1 is a diagram showing the use of my screen.

Figure 2 is a cross-sectional view through a portion of the screen.

Many different substances and mixtures have been tried in an eiort to obtain a screen which will not only transmit the light from the projector therethrough, but will define a clear-cut image on the side of the screen remote from the projector without the formation of a bright spot of light. I have found that these results may be 95 obtained by forming a screen` according to the following method.

For a base I preferably employ a substantially homogenous sheet of wood pulp formed in the following manner. The raw material may be fine wood pulp in anyconvenientI form. It may, for example, be shredded or in the form of saw-dust. This raw material is then digested by being cooked or boiled in a. suitable liquid, such as lime or sulphite, and this is best done under steam pressure. The result of this step is a loose, wet, brous mass of substantially homogenous material. This mass is then washed in water and bleached in any suitable manner and by any well-known means. The mass is still loose, wet and brous in character. l

I then add to the above mass a suitable agen as a fine clay or` lithopone to act as a diffuser and any desired color may be added at this stage in order to 'obtain the required shade.

will vary according to the amount of diffusion found-necessary for the particular screen being built, and the color will vary also and may be omitted altogether if desired.

The mass is thengolled out into sheets of the desired thickness 'and shape and dried. The

drying The .sheet formed in this manner is used as a The percentage of 'clay or lithopone base for the finished screen and I may apply thereto a coating of translucent diffusing material, this coating being formed in the following manner.

I first make a solution of air-dried soap chips in water, uns solution being formed by boiling. 6 I add tothis solution a second boiling solution of alum, the two being mixed when boiling or substantially at that temperature. The result of .this mixture is a dough-like mass. This mass is then pressed to force out the water-and it then easily di'sintegrates into a ne powder. This powder is then boiled in benzine, forming a liquid which I then apply in a thin film as a coating on one or both sides of the base. It is preferable to coat both sides as the coating is water-resistant and tough and thus protects the base as well as acting as diiusor.

In place of the coating just described above,

I may employ another coating made of a mixture of beeswax, linseed oil, gum copal and Venice turpentine. The linseed oil is used to thin out the beeswax and the turpentine thins out the gum copal. The mixture of the two solutions will form a coating which will have the desired characteristics. However, I prefer to form a coating of the material rst described above.

In the accompanying drawing I have shown at 1 a suitable projector which is adapted to project an image upon the screen 2, from which it is viewed from the position indicated at 3. The base is indicated at 4 in Fig. 2, and is preferably made in the manner described above. While'I have described the base as formed of wood pulp, it is obvious that equivalents of this material may be employed. IIhe essential thing is to have a base of cellulosic material in a translucent form. VThe base is then supplied with the coatings 5 and 6 onopposite sides thereof, al-

" though the coating on one side may be omitted if 9 sider myself entitled to all equivalents, and I 'v intend to limit myself only by the appended claims.

I claim:

1. A-trans1ucent projection screen comprising u()A a translucent base formed of wood pulp digested in lime to form a substantially homogenous mass, having a diffuser incorporated therewith, and a coating of translucent diffusing material thereon.

2. A translucent projection screen comprising a translucent base of wood pulp in a substantially homogenous mass having incorporated therein a fine clay, and a coating on said base formed of a solution of soap and alum in benzine.

3. A translucent projection screen comprising a base of substantially homogenous translucent cellulosic material having clay incorporated therein, and a coating of translucent diffusing material thereon.

4. A translucent projection screen comprising a translucent base`of Wood pulp in a substantially homogenous mass having incorporated therein a ne clay, and a diffusing coating comprising an insoluble soap on said base.

5. A translucent projection screen comprising a translucent base of Wood pulp in a substantially homogenous m'ass having incorporated therein a ne clay, and a diiusing coating comprising an aluminium soap on said base.

6. A translucent projection screen comprising a translucent base of substantially homogenous cellulosic material, and a diffusing coating comprising an insoluble soap on said base.

7. A translucent projection screen comprising a translucent base formed of Wood pulp in a substantially homogenous mass and a. coating of translucent diffusing material, comprising an aluminium soap on said base.

8. A rear projection screen comprising a translucent base formed principally of substantially homogeneous cellulosic material, a light-diffusing agent substantially uniformly incorporated in said screen base, and a second light-diiusing agent on an exterior surface of said screen, the quantity of said light-diffusing agents being approximately predetermined ,whereby a substantial amount of light traverses the screen when it is included in a rear projection system.

9. A rear projection screen comprising a base formed principally of substantially homogeneous cellulosic material, and light-diffusing means associated with said base to such limited extent that a substantial amount of light traverses the screen when it is included in a rear projection system, said light-diiusing means comprising a light-diiusing agent-on an exterior surface of said screen.

10. A rear projection screen comprising a base formed principally of substantially homogeneous cellulosic material, and light-diffusing means associated with said base to such limited extent that a substantial amount of light traverses the screen when it is included in a, rear projection system, said light-diffusing means comprising a light-diffusing agent substantially uniformly inorporated in and throughout said cellulosic maerial.

` ERNEST A. TROEGER. 

